MOLLUSCA OF THE ' CHALLENGER ' EXPEDITION. 599 



the umbilicus is defined by another whitish fillet, ornamented 

 with about thirty oblong beads. One or two smaller and more 

 faintly beaded threads lie within the edge of the umbilicus. 

 Longitudinals — there are of these on the last whorl about 120, 

 flexuous, marking the lines of growth, rather stronger, more 

 regular, and more distant than the spirals, which run over the 

 top of them and form little white nodes at the crossings. The 

 intersections of these two systems cut the whole surface into 

 rhombic reticulations, whose breadth is about 0-011 and their 

 height 0'006. The longitudinal threads themselves are about 

 O'OOS and the spirals about 0*003 broad. On the base the lon- 

 gitudinals are flattened and spread out into undulations. 

 Colour creamy, on a dull polished surface, with a very faint 

 nacreous gleam, which is pearly within the mouth ; the apex is 

 ruddy. Spire high and conical, with slightly concave slopes ; 

 apex broken. On the upper whorls the longitudinals are strong, 

 while the spirals are obsolete, except the carinal fillet, which 

 projects bluntly above the suture. Whorls about 14, of very 

 regular increase, very slightly convex, sharply acute-angled 

 at the carina ; on the base, flat at the outer edge and barely 

 convex in the middle, with a slight dip in toward the edge of 

 the umbilicus, which is strongly defined. Suture linear, de- 

 fined by the white carinal fillet, and also on the lower whorls 

 by being very slightly impressed. Mouth perpendicular, rhom- 

 boidal, the basal and palatal lines being parallel, the other two 

 somewhat diverging and curved, broader than high. Outer lip 

 sharp and thin, not patulous, not descending, with a shallow 

 open sinus below the suture, below this, about the middle of the 

 whorl, it advances with a rounded sweep, retreating sharply 

 across the carina to form the open rounded basal sinus towards 

 the outer edge of the base. JPillar-lip sharp and thin ; it 

 rises from the body a good way within the edge of the umbilicus. 

 It retreats so as to form a sinus, and there it bends over a little 

 on the umbilicus, and it forms a sharp angle projecting into a 

 tooth at the extreme point of the pillar. Umbilicus strong, 

 deep, abrupt, there being on the base only a very slight dip 

 in towards it, and it is defined by the white-beaded fillet. 

 Within, besides the two spiral lines, there are slight longi- 

 tudinal striations, and the inner edge of the whorls twines like 

 a staircase round it, but concealed by the over-curve of the 

 pillar-lip. H. 0-75. B. 0-65, least 0-6. Penultimate whorl 

 0-16. Mouth, height 0-2, breadth 0-28. 



